Implants such as spinal interbody fusion devices are used to treat degenerative disc disease and other damages or defects in the spinal disc between adjacent vertebrae. The disc may be herniated or suffering from a variety of degenerative conditions, such that the anatomical function of the spinal disc is disrupted. Most prevalent surgical treatment for these conditions is to fuse the two vertebrae surrounding the affected disc. In most cases, the entire disc will be removed, except for a portion of the annulus, by way of a discectomy procedure. A spinal fusion device is then introduced into the intradiscal space and suitable bone or bone substitute material is placed substantially in and/or adjacent the device in order to promote fusion between two adjacent vertebrae.
Spinal fusion devices may be inserted during a spinal surgical procedure using an anterior, posterior, posterior lateral, lateral or extrapedicular approach. Examples of expandable spinal interbody fusion devices are described in U.S. Pat. No. 6,595,998 entitled “Tissue Distraction Device”, which issued on Jul. 22, 2003 (the '998 Patent) and U.S. Pat. No. 7,967,867 entitled “Expandable Interbody Fusion Device”, which issued on Jun. 28, 2011 (the '867 Patent). Spinal fusion devices may also be non-expandable, monolithic devices of fixed dimension, as shown for example, in U.S. Pat. No. 7,749,269 which issued on Jul. 6, 2010 and is assigned on its face to Warsaw Orthopedic, Inc. (the '269 Patent) and U.S. Pat. No. 7,918,891 which issued Apr. 5, 2011 and is assigned on its face to NuVasive Inc. (the '891 Patent). The spinal fusion devices described in the '269 Patent and the '891 patent are particularly configured for insertion into the intradiscal disc space from the lateral approach, with such implants having a length that when positioned in the disc space from one lateral side to the other the implant may rest on the cortical rims of both opposing lateral sides of a vertebral body.
One of the issues facing a surgeon during spinal surgery is the proper positioning of the implant in the intradiscal disc space. Spinal fusion implants are frequently made of materials such as polyetheretherketone polymer (PEEK) for strength and other biocompatible properties. However, since such materials are often radiolucent they are difficult to visualize under X-rays or fluoroscopy. To enable visualization, a radiopaque material such as a metal marker or barium sulfate may be combined with the implant material when the implants are manufactured, such as described in the '998 Patent. Visualization elements may also be provided in the form of spike elements or pins located at the proximal and distal ends of the implant as well as in a medial support between fusion apertures, as shown, for example, in the '891 Patent.
While such known visualization have been generally satisfactory, there nevertheless remains a need for improvements in surgical techniques to assist the surgeon in determining the proper position of a spinal implant during the implantation procedure.